Solvent production



Patented July 28, 1942 SOLVENT PRODUCTION Jacquelin E. Harvey, Jr.,Atlanta, Ga., assignor of one-half to Southern Wood Preserving Company,East Point, Ga., a corporation of Georgia No Drawing. Application March14, 1941, Serial No. 383,470

Claims.

The present invention relates to the production of solvents from tarsand fractions thereof of aromatic content.

This application is a continuation in part of my application Serial No.345,436, filed July 13, 1940, for Production of an article of commerce,copending herewith, as to all matter common to the two applications.

An object of the present invention is the conversion of tars and/orfractions thereof of arcmatic content into solvents and/or plasticizers.

Another object of the present invention is the conversion of mixtures oftar fractions, while under influence of a catalyst, said catalyst havingat least partial sulfide content, into solvents and/or plasticizers.

Yet another object of the present invention is the substantially totalconversion of a mixture of tar fractions, by aid of catalysis, intosolvents and/or plasticizers, said conversion characterized by provisionof conditions that maintain said catalysis at substantially optimumconditions.

Other objects of the present invention will become apparent from thefollowing disclosures.

Usable starting materials of the present process include tars orfractions thereof, characterized by aromatic content. Said tars includedestructive distillation products of coal, as for instance, hightemperature coke oven tar, low temperature tar and gas house tar;aromatic extracts of coal and petroleum; high boiling aromatichydrocarbons produced by polymerization of petroleum or fractionsthereof, including gas and gases.

The present process provides a method for the conversion of tar/orfractions thereof, said tar and fractions thereof being characterized bythe presence of a multiplicity of rings, into solvents and/orplasticizers of superior aromaticity.

By the terms multiplicity of rings, ring multiples, or molecularcomplexes are meant those high boiling fractions, including pitch or tarfractions of aromatic content that may be viewed as having little or nosolvency or plasticity when compared to conventionallow boiling solventsor commercial plasticizers.

The molecular complexes necessitate step-wise treatment for conversionto the solvents and/or plasticizers of the present invention. By theterm step-wise is meant that when converting substantially the entiretyof starting material into the solvents and/or plasticizers of thepresent invention, said conversion is not effected in entirety by merelyonce impressing on the starting material the control variables of thepresent process, but rather is accomplished by repeatedly impressing theprocess controls, as hereinafter stated on said starting material. Theunconverted portion approaches zero as representing a maximumconversion; that is to say, the process controls of the present processare impressed on the starting material for conversion of a percentage,but less than the whole, into solvents and/ or plasticizers; afterremoval of said induced solvents and/or plasticizers by known methods,the unconverted portion, with or without addition of starting materialto compensate for product recovery, is again subjected to processcontrols for induction of said products, etc.

Viewed broadly, the present invention provides a process wherein thestarting materials are subjected to the action of hydrogen, undercatalyzed conditions characterized by said catalysis being maintained atoptimum conditions by specific provision, whereby to convert saidstarting material in aforesaid step-wise manner into solvents and/orplasticizers. The process of the present invention is furthercharacterized by being practiced in the liquid phase, as opposed tovapor phase that vaporizes substantially the entirety of the feed stock.The term liquid phase may not be technically correct, inasmuch asvarying amounts of the starting feed are vaporized; however, there is adefinite line of demarcation between the liquid phase herein used andthe commonly accepted vapor phase.

Among other things, the liquid phase hydrogenation of the presentprocess is employed for the following reason: that maintenance of liquidphase makes possible continued step-wise conversion to the end thatsubstantially volume for volume conversion be effected.

The following examples will serve to illustrate modes of practicing thegeneral principles upon which the practice of the present invention isbased, as well as the process of the present invention.

Example 1.-A coal tar fractions boiling substantially 3% at 380 C. waspassed through a high pressure reaction vessel while contacting asulphide catalyst and while simultaneously flowing hydrogentherethrough, at a pressure of 300 atmospheres and a temperature of 410C. Time of reaction one and one half hours. The beneficiated materialwas found to have an initial boiling point of substantially C. and wasdistilled to an upper limit of 200 C. to recover the distillate as asolvent of superior quality, that is to say, a solvent of substantially50% aromatic content, or more. The residue resulting from saiddistillation was fed back to the reaction vessel with crude startingmaterial.

At the end of the 36th hour of operation the synthesis of the solventhad declined. Research disclosed that the reason therefor was apparentat least partial conversion of the sulphide catalyst into some otherform. Identical operations were repeated using the same startingmaterial, except that the feed was adjusted to contain onehalf of onepercent sulphur. On the repeating operations the percentage of solventincrement held constant, other than normal loss normally anticipated dueto catalyst age. The beneficiated feed stock was stripped up to 200 C.for said solvent recovery and the residue therefrom being recycled tothe. end that substantially volume for volume of the starting materialbe converted, neglecting gasification and normal manufacturing loss, tothesolvent specified.

Thus the present example illustrates a process for converting instep-wise manner, a mixture of tar fractions substantially in theirentirety, into solvents of superior quality, characterized by saidconversion being effected in liquid phase, and further characterized bymaintenance, without substantial reduction, of original conversion ratioother than changes due to straightening-out or ageing of said sulphidecatalyst.

Concerning the addition of sulphur to the feed stock, the sulphurcontent of the starting material, including recycle :material, isadjusted to that sulphur content which will provide maintenance of thecatalyst in substantial sulphide form. Thus, forming an important partof the present invention is the maintenance of a hydrogen sulphidepartial pressure of at least a fractional atmosphere, or as high as oneatmosphere, or higher. A few trials will readily disclose that hydrogensulphide partial pressure that will maintain the catalyst in substantialsulphide form under given conditions.

-Of course, the sulphur may be supplied in forms other than elementalsulphur. Sulphur may be added in any form capable of generating hydrogensulphide to the end that the catalyst be maintained in substantialsulphide form.

Some tars, or fractions thereof, including aromatic extracts ofpetroleum or petroleum fractions and polymerization products thereof,may have suflicient sulphur or sulphur compound therein to obviate thenecessity of sulphur addition.

Thus, it will be seen that the invention pro vides a process for theconversion, substantially volume for volume, vof a mixture of tarfractions into solvents of superior quality, said conversion beingcharacterized by subjecting the starting material in liquid phase to theaction of hydrogen and hydrogen sulphide, said hydrogen sulphiderepresenting a partial pressure of at least a fractional atmosphere;said conversion being further characterized by the presence of asulphide catalyst maintained in substantial sulphide form, the whilecatalyzing step-wise reduction .to substantially total conversion asaforesaid.

Earample 2.Coal tar 'pitchboi'ling substantially 15% .at 355 C. waspassed through a high pressure reactor, while simultaneously flowinghydrogen therewith. Catalyst, molybdenum sulphide. Pressure .300atmospheres and temperature 400 C. Hydrogen sulphide partial pressure 1atmosphere and gas flow in excess of 4,000 cubic feet per barrel feed.Reaction time was 1 hour. The

beneficiated material after being relieved of its dissolved and occludedgas was returned to the reaction system and treated under identicalconditions, except the temperature was raised to 425 C. The twicebeneficiated material was distilled to an upper limit of 290 C. torecover the solvent which had an overall aromaticity of more than 50%and distilled predominantly between 150 C. and 292 C. The solvent soproduced may be fractionally cut to provide solvents of varied boilingranges.

After the starting material has been subjected to the process controlsfor solvent induction, the point at which the fractional cut is made forsolvent recovery is not an inflexible point, but is rather varied bydesired end point of the recovered solvent. In the following tabulardata are shown end points of various commercial solvents, substitutesfor which may be provided by the induced solvents of the presentprocess.

Solvents Identification: Endpoint, degrees C. Benzol Toluol Hi-flashnaphtha 200 Heavy naphtha 290 High boiling crudes and plasticizers 360Other end points may be provided.

When recovering the solvents of the .present invention from thebeneficiated material, as for instance, when recovering the solvent toan upper limit of 360 C., the fractional part boiling ,between (as anexample) 300 C. and 360 C. may be used as .a plasticizing oil, or thelike because of induced characteristics.

Example 3.Coal tar, boiling predominantly above C. was subjected to theaction of hydrogen and hydrogen sulphide at 400 C. for one half hour.Catalyst was molybdenum and tin sulphide, pressure 400 atmospheres andhydrogen sulphide partial pressure substantially 1 atmospheres. Thebeneficiated material Was then subjected to a second treatment underidentical conditions, except that the temperature was raised to 450 C.and treatment continued for 1 hour. The beneficiated mass was thendistilled to an upper limit of 290 C. to recover the solvent as adistillate. The residue therefrom wasadded to fresh starting tar andrecycled; sulphur content being adjusted. The solvent so recovered hadan arcmaticity of greater than 50%.

Example 4.It has been discovered that when subjecting certain mixturesof refined coal tar fractions to the action of hydrogen in accordancewith the present process for the production of solvents and/orplasticizers that the formerly accepted teaching that product increment,depolymerization and/or hydrogen absorption are linear functions of thetime, is not followed.

When subjecting a mixture of crude coal tar fractions boilingpredominantly above 250 C. or 275 C. to the action of hydrogen, researchhas disclosed that the newly induced products, depolymerization and/orhydrogen absorption are linear functions of the time. As an example,when the above mixture of crude coal tar fractions is subjected to theaction of hydrogen for 2, 5-, and 8-hour periods, the newly inducedproducts, depolymerization and/or hydrogen absorption are linearfunctions of the time element One of the preferred starting materials ofthe present process is a mixture of refined coal tar fractions boilingpredominantly above 355 or 380 C. Such a starting material isconveniently the final residue resulting from evaporating coal tar todryness or substantial dryness and. then stripping wood preservativefrom the distillate. This final residue mass of refined tar fractions isan especially suitable refined coal tar ,pitch to be used as startingmaterial of the present process. However, in contradistinction to themixture of crude coal tar fractions boiling predominantly above 250 or300 C., when the aforenamed preferred starting material is subjected tothe action of hydrogen for production of solvents and/ or plasticizers,the newly induced frac tions, depolymerization and/ or hydrogenabsorption are not, as described for the other mixture of crude coal tarfractions, linear functions of the time. A critical period of treatmentby or with hydrogen exists, and which if exceeded causes loss of newlyinduced fractions, polymerization and/or lessened hydrogen absorption oncertain fractions of the preferred starting material under treatment.

The critical time element because of the obvious possible variations inthe characteristics of the aforenamed refined coal tar pitch cannot bespoken of as an arbitrary figure. It can be stated, however, that if therefined pitch were to be subjected to the action of hydrogen for such alength of time, which for the other crude tar fractions would illustratethat the newly induced fractions, depolymerization and/or hydrogenabsorption were linear functions of the time element, loss of inducedproducts, polymerization and/or lessening of hydrogen absorption wouldoccur. When treating the refined coal tar pitch by or with hydrogen, thecritical time element is in the order of about three hours.

In the disclosures made herein and in the appended claims distillateremoval of low boiling portions from the beneficiated material isconsidered and the equivalent of fractional removal by gas movement,solvent action or the like. The converse also obtains.

In accordance with the present process the refined pitch is passedthrough a high pressure reaction vessel while simultaneously flowinghydrogen and hydrogen sulfide therewith; catalyst molybdenum sulfide andtime of contact two hours; hydrogen fiow 15,000 cubic feet per barrelfeed stock; total pressure 500 atmospheres.

The beneficiated refined coal tar pitch is characterized by loweredspecific gravity, viscosity and coke residue, and the high boilingfraction relatively susceptible to thermal degradation will, at least toa degree, be rendered thermally stable. Too, the beneficiated materialas flowing from the period of hydrogen action specified will provideconformance to the accepted teaching that the newly induced fractions,depolymerization and/or hydrogen absorption are linear functions of thetime element, whereas if an attempt were made to secure additionalincrement of newly induced fractions, depolymerization and/or hydrogenabsorption by an extended period of time, as for instance in excess ofabout three hours, the newly induced fractions, depolymerization and/orhydrogen absorption would not be linear functions of the time element.Among other things, there would be an actual loss of newly inducedfractions. The beneficiated material is distilled to an upper limit of,as an example, 360 C. to recover as distillate the fraction boilingbelow 300 C. as a superior solvent having at least in the order of 50%ring structures, and the fraction BOO-360 C. characterized bypreponderance of ring structures and having for certain purposesplasticizing properties induced therein by the process. In lieu ofrecovering the plasticizer as a distillate, it may be recovered as aresidue incidental to the recovery of the aforementioned solvent, which,if desired may be fractionated to recover superior solvents of variousboiling ranges. In recovering the plasticizer as a residue, theplasticizer represents as an example, the entirety of the beneficiatedrefined coal tar pitch boiling above 300 C.

Another variation of practicing utilization of the refined coal tarpitch is first depolymerizing it, at least to a degree by use of asolvent of aromatic content as for instance one having an aniline pointof not in excess of 50 C. Small amounts of solvents are helpful, and upto volume for volume, or more, may be employed. Thereafter the solventand solute are subjected to the action of hydrogen in accordance withthe present process.

When subjecting the refined pitch to the action of hydrogen in thepresence of a sulfide catalyst, unless there is maintained a hydrogensulfide partial pressure in the order of at least a fractionalatmosphere reaction conditions are not sustained, but are characterizedby a diminution.

Yet another variation of the process that utilizes the refined coal tarpitch having a critical time element as explained in the foregoing, isto separate the material into narrow boiling cuts, and then with orwithout employment of a solvent as aforedescribed, subject the narrowboiling fractions to the action of hydrogen in accordance with theprocess. The narrow boiling cuts may be provided having, as an example,a range of 20 C., or more. If desired, following the hydrogen action anydesired form of chemical refining may be employed.

In order to preclude undesired reactions when treating the refinedpitch, hydrogen flows are held in excess of 3000 cubic feet per barrelof material treated.

The liquid phase of the present invention, as heretofore explained, isused for the reason that only in liquid phase can step-wise reduction ofsubstantially volume for volume of the starting material be effected tosolvents of superior solverrcy.

Continuous or batch methods may be used, In the event continuousconversion is practiced, conversion may be effected in a single reactor,a series of reactors, a parallelism of reactors, including amultiplicity thereof. When practicing continuous methods whereinhydrogen or hydrogen-containing gas flows in a stream, varying amountsof said gas may be used, dependent upon results desired. However, thefiow of gas is always held, at least, slightly in excess of that amountwhich induces appreciable carbonaceous increment, which increment is,however, not to be confused with that carbonaceous increment that isinherent to the process and which usually causes plant shut-down, as anexample, every 3 to 6 or 9 months, or longer. The gas flow, usingaverage tars, or fractions thereof, is desirably held. in excess of3,000 cubic feet per barrel material treated.

By the term beneficiated as used herein and in the appended claims ismeant starting material at least once subjected to the action ofhydrogen.

Tar, or fractions thereof, that have had their carbon content loweredare especially adapted to be used as starting materials of the presentprocess, and the claims are to be read with this disclosure in mind. Theterms tar and tar fractions as used herein and in the appended claimsare meant to cover :said tar and/or tar fractions up to substantiallythe time of actual conversion into solvents of the present invention.

The process variables are adapted to various coordinations to producelow boiling solvents and/or high boiling sol-vents. Excessive timeelement may be substituted for increased temperatures in some cases whenproducing additional solvent increment and/or lower boiling ends.

As is well known, hydrogenations proceed at moderate temperatures andpressures; however, to approximate commercial necessities, elevatedtemperatures and pressures are desirable. Femperatures as low as 250 C.and pressures as low as 50 atmospheres are usable; however, withcatalysts now commercially available, the necessity of inordinately longperiods of treatment makes higher temperatures and pressures desirable.With pressures of 200 atmospheres and above, and temperatures of 375 C.and above, when converting as aforenamed in said catalyzed manner, goodresults have been obtained.

However, as mentioned in the foregoing a control of process variables isdesired that causes no coking.

Catalysts assist in speeding and directing the desired reactions of theprocess of the present invention. All hydrogenating catalysts ofsulphide form are usable. However, catalysts other than of sulphide formmay be provided, with subsequent conversion to the sulphide or:partially sulphide form due to the action of supplied hydrogensulphide. Various catalysts in conjunction with those aforementioned maybe used, such as in various shapes; deposited in well known manner oncarriers; cobalt, tin, vanadium, molybdenum, chromium, tungsten, ortheir compounds; promoted or not; in admixture if desired, with orwithout small amounts of acid, acids, halogen or derivatives ofhalogens; all sulphide catalysts of hydrogenating efli'cacy, in the formof shapes, pellets, extruded lengths, comminuted, with or without thepresence of other materials possessing hydrogenating properties, or not;such as asbestos, quartz, earths, lumps of brick, etc.

By the term superior solvency as used herein and in the appended claimsis meant that the solvents of the present process are of greatersolvency than hydrocarbon solvents commercially available, and have,among other things, an aromaticity of in the order of 50%, or greater.

When adjusting the sulphur content of the feed stock, including recyclematerial, so as to provide that hydrogen sulphide partial pressurenecessary for maintenance of at least a portion of the catalyst insulphide form, the sulphur may be added as elemental sulphur, or anyform of sulphur capable of providing aforesaid requirement. Some of thefeed stocks may, however, contain sufiicient sulphur without additionthereto.

At times when using as starting material tar fractions that contain alarge percentage of molecular complexes, it may be desirable to at leastpartially depolymerize said molecular complexes by addition of a solventthereto.

From the foregoing disclosure it will be seen that the present processprovides a method for converting tar, or fractions thereof, intosolvents, said conversion being characterized by subjecting said tar,and/or fractions thereof, while .in liquid phase in the presence of asulphide catalyst to the action of hydrogen and hydrogen sulphide withtime, temperature and pressure so controlled as to produce solventincrement, and recovering from the beneficiated material a .solventhaving an aromaticity of in the order of 50% or greater.

The evaluation of solvent power is conveniently accomplished by findingthe well-known aniline point of kauri-butanol number. The evaluation ofplasticizing .properties is conveniently accomplished by recourse tomethods suggested in chapter VI, The technology of ;solvents by Dr. OttoJordon, Mannheim, Germany, translated by Alen D. Whitehead, ChemicalPublishing Company of New York, Incorporated, New York, New York.

Minor changes may be made in the details of the foregoing withoutdeparting from the spirit of the invention.

I claim:

1. In the production of a solvent from the refined pitch produced bystripping high temperature coal tar to at least about substantial:dryness, and fractionating the overhead material to recover a liquiduseful as .a wood preservative, and a higher boiling fraction boilingpredominantly above 355 C., the process which comprises: subjecting saidhigher boiling fraction while contacting a sulfide catalyst to .theaction of hydrogen and hydrogen sulfide at a pressure and temperature inexcess of about 200 atmospheres and 375 C., respectively, for a periodnot in excess of about three hours, whereby to avoid loss of newlyinduced fractions to provide a solvent.

2. In the production of a solvent from .the refined pitch produced bystripping high temperature coal tar to at least about substantialdryness, and fractionating the overhead material .to recover a liquiduseful as a wood preservative, and a higher boiling fraction boilingpredominantly above 355 C., the process which comprises: subjecting saidhigher boiling fraction, while contacting a sulfide catalyst, to theaction of hydrogen and hydrogen sulfide for a period not in excess ofabout three hours, whereby to avoid loss of newly induced fractions; andfractionating the beneficiated material to provide low boiling fractionsas a solvent.

3. The process of claim '2 with the inclusion of recycling the residue.

4. In the production of a solvent from the refined pitch produced bystripping high temperature coal tar to at least about substantialdryness, and fractionating the overhead material to recover a liquiduseful as a wood preservative, and a higher boiling fraction boilingpredominantly above 355 C., the process which comprises: subjecting saidhigher boiling fraction, while contacting a sulfide catalyst, to theaction of hydrogen and hydrogen sulfide at a pressure in excess of about50 atmospheres and a .temperature in excess of about 375 C. for a periodnot in excess of about three hours, whereby to avoid polymerization, toproduce a solvent.

5. In the production of a solvent from the refined pitch produced bystripping high temperature coal tar to at least about substantialdryness, and fractionating the overhead material to recover a liquiduseful as a wood preservative, and a higher boiling fraction boilingpredominantly above 355 C., the process which com prises: subjectingsaid higher boiling fraction,

while contacting a sulfide catalyst, to the action of hydrogen andhydrogen sulfide at a temperature and pressure in excess of 250 C. and50 atmospheres, respectively, for a period not in excess of about threehours, whereby to avoid lowered hydrogen absorption, to provide asolvent.

6. The process of producing a solvent which comprises: evaporating hightemperature coal tar to at least about substantial dryness;fractionating the overhead material to recover a liquid useful as a woodpreservative, and a higher boiling fraction boiling predominantly above355 C.; and subjecting said higher boiling fraction, while in thepresence of a sulfide catalyst, to the action of hydrogen and hydrogensulfide at a pres sure and temperature in excess of 200 atmospheres and375 C., respectively, for a period not in excess of about three hours,whereby to avoid loss of newly induced fractions, to produce a'solvent.

7. The process of producing a solvent which comprises: evaporating hightemperature coal tar to at least about substantial dryness;fractionating the overhead material to recover a liquid useful as a woodpreservative, and a higher boiling fraction boiling predominantly above355 C.; and subjecting said higher boiling fraction, while contacting asulfide catalyst, to the action of hydrogen and hydrogen sulfide for aperiod not in excess of about three hours, whereby to avoid loss ofnewly induced fractions; and fractionating the beneficiated material toprovide low boiling fractions as a solvent.

8. The process of claim 7 with the inclusion of recycling the residue.

9. The process of producing a solvent which comprises: evaporating hightemperature coal tar to at least about substantial dryness;fractionating the overhead material to recover a liquid useful as a woodpreservative, and a higher boiling fraction boiling predominantly above355 0.; and subjecting said higher boiling fraction, While contacting asulfide catalyst, to the action of hydrogen and hydrogen sulfide at apressure and temperature in excess of about 200 atmospheres and 375 C.,respectively, for a period not in excess of about three hours, wherebyto avoid polymerization, to produce a solvent.

10. The process of producing a solvent which comprises: evaporating hightemperature coal tar to at least about substantial dryness;fractionating the overhead material to recover a liquid useful as a woodpreservative, and a higher boiling fraction boiling predominantly above355 (3.; and subjecting said higher boiling fraction, while contacting asulfide catalyst, to the action of hydrogen and hydrogen sulfide at atemperature and pressure in excess of about 250 C. and atmospheres,respectively, for a period not in excess of about three hours, wherebyto avoid lowered hydrogen absorption, to produce a solvent.

JACQUELIN E. HARVEY, JR.

